DNA, RNA, and Protein Synthesis

1. DNA, RNA, andProtein Synthesis Chapter 12

2. Historical Perspectives Debrief using the DNA Research and Structure Summary

3. Heat-killed, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Harmless bacteria (rough colonies) Control(no growth) Heat-killed, disease-causing bacteria (smooth colonies) Disease-causing bacteria (smooth colonies) Dies of pneumonia Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies) Fred Griffith (1928) • discovered transformation - one form of bacteria was transformed into another form …perhaps by a gene.

4. Oswald Avery (1944) • Avery expanded on Griffith’s experiment by destroying various compounds with ____________ and seeing if transformation occurred • found that __________ (not protein) is the genetic material

5. Hershey and Chase (1952) • Radioactively labeled the PROTEIN of a virus with sulfur and the DNA of a virus with phosphorus • After the virus transmitted genetic material into the bacteria cell, radioactive phosphorus was found in the cell • Means the genetic material is DNA

6. Chargaff

7. Rosalind Franklin • Saw X-shaped pattern with X-ray diffraction

8. Watson and Crick • Published article on DNA structure based on Franklin’s x-rays • Credited with the discovery of the “double helix”

9. Structure of Deoxyribonucleic acid (dna)

10. DNA is made of subunits called nucleotides • Nucleotides have 3 parts: • Deoxyribose sugar (5-carbon, pentagon shaped) • Phosphate group • Nitrogen base – 4 nitrogen bases in 2 categories • Purines: adenine and guanine - double-ringed structure • Pyrimidines: thymine and cytosine - single-ringed structure

11. Purines Pyrimidines Adenine Guanine Cytosine Thymine Deoxyribose Sugar Phosphate group nucleotide Pg 291

12. Nucleotide Hydrogen bonds Sugar-phosphate backbone • DNA shape is double stranded, called a “Double Helix” • sugars and phosphates alternate forming the backbone with covalent bonds • bases attach in center by weak hydrogen bonds • Adenine always bonds with Thymine • Guanine always bonds with Cytosine Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Pg 294

13. Use the base pairing rules to predict what the complementary strand of DNA would be Original strand= A G G T C C T A Complementary strand= • The amount and order of bases determines genes • DNA has the same molecular structure in all organisms but • single circular strand of DNA in prokaryotes • DNA in the form of X-shaped chromosomes in eukaryotes

14. DNA Replication

15. DNA Replication • Occurs in nucleus • Because strands are complementary, each strand serves as a template for a new strand

16. Steps in Replication • Helicase (an enzyme) causes DNA to unwind then unzip by breaking hydrogen bonds between base pairs • Each strand serves as a template for the attachment of a NEW complementary strand by bringing in new base pairs • The enzyme DNA polymerase joins the new bases and DNA recoils

17. Replication is “semi-conservative”-each double stranded DNA molecule is composed of one new strand & one old strand Original strand DNA polymerase New strand pg298 Growth DNA polymerase Growth Replication fork Replication fork Nitrogenous bases New strand Original strand

18. RNA – Ribonucleic Acid

19. How is RNA different from DNA? • Single stranded • Ribose sugar • Uracil (U) instead of Thymine Three types of RNA • messenger RNA (mRNA)-carries instructions for assembling proteins from DNA to the ribosome • transfer RNA (tRNA)-brings amino acids to the ribosome • ribosomal RNA (rRNA)-component of ribosome

20. Transcription How does the message in DNA get to the ribosome?

21. Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNApolymerase DNA RNA Transcription • copying info from one form to another (DNA RNA) • occurs in nucleus before protein synthesis • DNA is unzipped by enzymes • mRNA copy of the DNA is made by bases pairing • After completion, mRNA breaks off—DNA strands rejoin after transcription • mRNA leaves nucleus and travels to ribosome for protein synthesis

22. The Genetic Code

23. The Genetic Code • Portions of DNA, called genes, code for proteins which control ______. • Not all DNA codes for proteins • exons-segments of DNA that are “expressed” • introns-segments of DNA that are not expressed and are edited out of mRNA How do genes code for amino acids?

24. codon-each set of three consecutive nucleotides that codes for a specific amino acid • There are 64 possible codons (43) for 20 amino acids • 61 code for amino acids, 3 code as “stop” codons • each codon codes for a specific amino acid, but some amino acids are coded for by more than one codon

25. Examples: Which amino acid is coded for by the following mRNA codons? • AAA • AGA • GAU • UAG Which codon(s) code(s) for the following amino acids? • Valine • Histidine • Serine • Isoleucine

26. Translation: Protein Synthesis

27. Translation (protein synthesis) • occurs at the ribosome • putting the info into a new language (RNA  Protein) • Converts the information in a sequence of nitrogenbases in mRNA into a sequence of aminoacids that make up a protein

28. Steps in Translation • mRNA attaches to a ribosome • The ribosome has 2 bonding sites for tRNA • tRNA brings amino acids to the ribosome • tRNA is a loop shaped structure with three bases called the anticodon (complementary to the codon) and a specific amino acid attached to it • AUG is the “start codon” for protein synthesis. Draw the tRNA that will bond to this codon.

29. Nucleus Messenger RNA Messenger RNA is transcribed in the nucleus. Lysine Phenylalanine tRNA Methionine Ribosome Start codon mRNA

30. Steps in Translation • The ribosome attaches the amino acids on tRNA by peptide bonds to form a protein that is ready to be used by the cell Lysine tRNA mRNA Translation direction Ribosome

31. Steps in Translation • The ribosome moves down the mRNA strand by codons attaching amino acids to the protein Growing polypeptide chain Ribosome tRNA mRNA

32. Gene Mutations

33. Gene Mutations • any mistake in DNA is a mutation • source of evolution, genetic disorders, cancer, etc. • can be random, can be caused by environmental factors • x-rays, chemicals, radioactive substances, UV light Two types of gene mutations: • point mutation-change in a single base pair in DNA sequence (also called a substitution) • some do not impact protein function, others are disastrous

34. ex of point mutation THE CAT ATE THE RAT Replace this letter with a C. What happens? THE CAT CTE THE RAT What if the 6th DNA nucleotide was changed instead of the 5th?

35. Gene Mutations (CONT) • frameshift mutation-results from the addition (insertion) or deletion of a single base pair. • Proteins resulting from these mutations are rarely functional and usually disastrous

36. ex of frameshift mutations (insertion and deletion) THE CAT ATE THE RAT DELETE this “A”. What happens? THE CAT TET HER AT The “reading” frame shifts. THE CAT ATE THE RAT INSERT the letter “G”. What happens? THE CAT GAT ETH ERA T The reading frame shifts.